1. Field of the Invention
The present invention relates generally to a variable valve control apparatus and method for an internal combustion engine provided with a variable valve mechanism which varies valve characteristics, such as a variable valve timing mechanism which varies opening/closing timing of an engine valve (intake valve/exhaust valve).
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 10-153104 discloses a variable valve timing mechanism having a configuration in which a rotation phase of a camshaft relative to a crankshaft in an internal combustion engine is changed by the braking of an electromagnetic brake or a solenoid brake so that opening/closing timing of an engine valve is varied.
In the variable valve timing mechanism described above, since the rotation phase is determined by the balance of the torque in an advance angle direction by an electromagnetic force of the electromagnetic brake with the torque in a retarded angle direction by a return spring, the rotation phase might be changed by the inertia torque generated when an engine rotating speed is changed.
Although the rotation phase changed as in the above manner is converged into a target value by a feedback control, it takes much time until the rotation phase is converged. Therefore, there is a problem of degradation in combustion performance due to a phase change during the convergence.